In recent years liquid detergents have become widely accepted for cleaning hard surfaces, e.g., painted woodwork and panels, tiled walls, wash bowls, bathtubs, linoleum or tile floors, washable wall paper, etc.. Such liquids comprise clear and opaque aqueous mixtures of water-soluble synthetic organic detergents and water-soluble detergent builder salts. In order to achieve comparable cleaning efficiency with granular or powdered all-purpose cleaning compositions, use of water-soluble inorganic phosphate builder salts was favored in the prior art all-purpose liquids. For example, such early phosphate-containing compositions are described in U.S. Pat. Nos. 2,560,839; 3,234,138; 3,350,319; and British Patent No. 1,223,739.
In view of the environmentalist's efforts to reduce phosphate levels in ground water, improved all-purpose liquids containing reduced concentrations of inorganic phosphate builder salts or non-phosphate builder salts have appeared. A particularly useful self-opacified liquid of the latter type is described in U.S. Pat. No. 4,244,840.
However, these prior art liquid detergents containing detergent builder salts or other equivalent tend to leave films, spots or streaks on cleaned unrinsed surfaces, particularly shiny surfaces. Thus, such liquids require thorough rinsing of the cleaned surfaces which is a time-consuming chore for the user.
In order to overcome the foregoing disadvantage of the prior art, U.S. Pat. No. 4,017,409 teaches that a mixture of paraffin sulfonate and a reduced concentration of inorganic phosphate builder salt should be employed. However, such compositions are not completely acceptable from an environmental point of view based upon the phosphate content. On the other hand, another alternative to achieving phosphate-free all-purpose liquids has been to use a major proportion of a mixture of anionic and nonionic detergents with minor amounts of glycol ether solvent and organic amine as shown in U.S. Pat. No. 3,935,130. Again, this approach has not been completely satisfactory and the high levels of organic detergents necessary to achieve cleaning cause foaming which, in turn, leads to the need for thorough rinsing which has been found to be undesirable to today's consumers.
Another approach to formulating hard surface liquid detergent compositions where product homogeneity and clarity are important considerations involves the formation of oil-in-water (o/w) microemulsions which contain one or more surface active detergent compounds, a water-immiscible solvent (typically a hydrocarbon solvent), water and a "cosurfactant" compound which provides product stability. By definition, an o/w microemulsion is a spontaneously forming colloidal dispersion of "oil" phase particles having a particle size in the range of about 25 to about 800 .ANG. in a continuous aqueous phase. In view of the extremely fine particle size of the dispersed oil phase particles, microemulsions are transparent to light and are clear and usually highly stable against phase separation.
Patent disclosures relating to use of grease-removal solvents in o/w microemulsions include, for example, European Patent Applications EP 0137615 and EP 0137616--Herbots et al; European Patent Application EP 0160762--Johnston et al; and U.S. Pat. No. 4,561,991--Herbots et al. Each of these patent disclosures also teaches using at least 5% by weight of grease-removal solvent.
It also is known from British Patent Application GB 2144763A to Herbots et al, published Mar. 13, 1985, that magnesium salts enhance grease-removal performance of organic grease-removal solvents, such as the terpenes, in o/w microemulsion liquid detergent compositions. The compositions of this invention described by Herbots et al. require at least 5% of the mixture of grease-removal solvent and magnesium salt and preferably at least 5% of solvent (which may be a mixture of water-immiscible non-polar solvent with a sparingly soluble slightly polar solvent) and at least 0.1% magnesium salt.
However, since the amount of water immiscible and sparingly soluble components which can be present in an o/w microemulsion, with low total active ingredients without impairing the stability of the microemulsion is rather limited (for example, up to about 18% by weight of the aqueous phase), the presence of such high quantities of grease-removal solvent tend to reduce the total amount of greasy or oily soils which can be taken up by and into the microemulsion without causing phase separation. The following representative prior art patents also relate to liquid detergent cleaning compositions in the form of o/w microemulsions: U.S. Pat. Nos.. 4,472,291--Rosario; 4,540,448--Gauteer et al; 3,723,330--Sheflin.
Liquid detergent compositions which include terpenes, such as d-limonene, or other grease-removal solvent, although not disclosed to be in the form of o/w microemulsions, are the subject matter of the following representative patent documents: European Patent Application 0080749; British Patent Specification 1,603,047; 4,414,128; and 4,540,505. For example, U.S. Pat. No. 4,414,128 broadly discloses an aqueous liquid detergent composition characterized by, by weight:
(a) from about 1% to about 20% of a synthetic anionic, nonionic, amphoteric or zwitterionic surfactant or mixture thereof; PA1 (b) from about 0.5% to about 10% of a mono- or sesquiterpene or mixture thereof, at a weight ratio of (a):(b) lying in the range of 5:1 to 1:3; and PA1 (c) from about 0.5% about 10% of a polar solvent having a solubility in water at 15.degree. C. in the range of from about 0.2% to about 10%. Other ingredients present in the formulations disclosed in this patent include from about 0.05% to about 2% by weight of an alkali metal, ammonium or alkanolammonium soap of a C.sub.13 -C.sub.24 fatty acid; a calcium sequestrant from about 0.5% to about 13% by weight; non-aqueous solvent, e.g., alcohols and glycol ethers, up to about 10% by weight; and hydrotropes, e.g., urea, ethanolamines, salts of lower alkylaryl sulfonates, up to about 10% by weight. All of the formulations shown in the Examples of this patent include relatively large amounts of detergent builder salts which are detrimental to surface shine. PA1 (a) 15% to 36%, preferably 18% to 34%, of a mixture of a magnesium metal salt of a C.sub.13 -C.sub.17 alkyl sulfonate surfactant; PA1 (b) 1% to 20%, more preferably 2% to 18% of an alkali metal salt or ammonium salt of a C.sub.8 -C.sub.18 alkyl polyethenoxy sulfate surfactant, wherein the ratio of sulfonate surfactant to the sulfate surfactant is about 8:1 to about 1:8, more preferably about 7:1 to about 1:2; PA1 (c) 0.5% to about 10%; more preferably 1% to 5% of an alkyl polyglucoside surfactant; PA1 (d) 0.4% to 10.0%, more preferably 2.0% to 7.0% of a perfume, an essential oil or a water insoluble hydrocarbon; PA1 (e) 1% to 25%, more preferably 2 to 8% of a cosurfactant; PA1 (f) 0 to 5%, more preferably 0.1 to 3% of at least one hydrotrope; PA1 (g) 0 to 4%; more preferably 0.1 to 2% of magnesium sulfate; PA1 (h) 0.5% to 5%, more preferably 0.5 to 3% of an alkyl monoalkanol amide and/or an alkyl dialkanol amide and mixtures thereof; and PA1 (i) the balance being water, wherein the composition has a Brookfield viscosity at 25.degree.C. at 3 rpms using a #18 spindle spindle of about 20 to 500 cps, more preferably about 100 to 450 cps, a pH of about 5 to about 7, and a light transmission of at least about 95%, more preferably at least about 98%. Explicitly excluded from the instant compositions are nonionic surfactants which are the condensation product of an organic aliphatic or alkyl aromatic hydrophobic compound and hydrophilic ethylene oxide and/or propylene oxide groups, zwitterionic surfactant such as a betaine surfactant straight chain C.sub.12-16 mono olefin sulfonate surfactants, cationic surfactants and grease release agents consisting of ##STR1## wherein R.sub.1 is a methyl group and R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of CH.sub.3, C.sub.2 H.sub.5, CH.sub.2 CH.sub.2 Y, wherein Y is selected from the group consisting of Cl, Br, CO.sub.2 H.sub.1, (CH.sub.2 O).sub.n OH, wherein n is 1 to 10 and OH and X is selected from the group consisting of Cl, Br, methosulfate and HCO.sub.3 such as choline chloride. The weight ratio of the magnesium salt of the C.sub.10-16 linear alkyl benzene sulfonate surfactant to the alkyl polyglucoside surfactant is at least 12:1 preferably 15:1 and the weight ratio of the magnesium salt of the C.sub.10-16 linear alkyl benzene sulfonate surfactant plus the metal or ammonium salt of the alkyl ether polyethenoxy sulfate surfactant to the alkyl polyglucoside surfactant is at least 15:1 and more preferably 18:1.
Furthermore, the present inventors have observed that in formulations containing grease-removal assisting magnesium compounds, the addition of minor amounts of builder salts, such as alkali metal polyphosphates, alkali metal carbonates, nitrilotriacetic acid salts, and so on, tends to make it more difficult to form stable microemulsion systems.